Networking may be straightforward, but the world of networking terminology is not. I’ve been steeped in the strange lingo of Ethernet for many years, but I still get confused by some of the terms. What’s the difference between 1000BASE-CX, 1000BASE-SX, and 1000BASE-T? In this post, I’m going to tackle this Ethernet network naming convention.

Networking Basics

Let’s get the first two components of the network name out of the way:

The  first part  is the signaling rate in megabits per second. In layman’s terms, this is  the speed of the network  at hand. You are likely to come across one of the following:

  • 10 megabits
  • 100 megabits – Fast Ethernet
  • 1000 megabits – Gigabit Ethernet, GbE, or 1000BASE-X
  • 10,000 megabits – 10 Gigabit Ethernet, 10GbE, or 10GBASE-X
  • 40,000 megabits – 40 Gigabit Ethernet, 40GbE, or 40GBASE-X
  • 100,000 megabits – 100 Gigabit Ethernet, 100GbE, or 100GBASE-X

It may strike you as odd that the next part is always the word, “BASE”. But there is a reason for this, too.BASE refers “baseband”, meaning that this is an unfiltered line not requiring a digital modulation scheme. Back in the day, there was a 10PASS-TS version of Ethernet that used a signaling scheme similar to a modem, but baseband is dominant today.

So 100BASE refers to a Fast Ethernet connection that uses the unfiltered cable for transmission.


The third part of an Ethernet network type refers to the cabling  used to carry the signals. The earliest forms of Ethernet used coaxial cable, but thin twisted-pair cabling became popular in the mid-1990s. Faster versions of Ethernet also often use fiber optics rather than electrical signals.

There are a bewildering assortment of physical interconnects for Ethernet. But the naming system isn’t as complex as it might appear:

  • The first letter tells us which kind of wire we are talking about:
    • “T” means twisted-pair cable (e.g. the common Cat5 in use today)
    • “K” means a copper backplane
    • “C” means balanced copper cable
    • “F” means optical cable
    • “B” uses two wavelengths over a single optical cable
    • “S” means short-range multi-mode optical cable (less than 100 m)
    • “L” means long-range single- or multi-mode optical cable (100 m to 10 km)
    • “E” means extended-range optical cable (10 km to 40 km)
    • “Z” means long-range single-mode cable at a higher wavelength
  • Next is the coding scheme for data on the wire
    • “X” means 4B/5B block coding for Fast Ethernet or 8B/10B block coding for Gigabit Ethernet
    • “R” means 64B/66B block coding
  • Finally, we have a number representing the number of parallel “lanes” for data
    • “1” would mean serial (non-parallel) but is omitted instead
    • “4” or “10” are available for copper wire
    • Just about any other number could be used for optical lanes or wavelengths


Now let’s look at some examples:

  • Back in the day,  10BASE-T  became more common than coaxial  10BASE2. It was a simple 10 megabit baseband signal over common twisted-pair.
  • When Fast Ethernet first rolled out, there was some concern that traditional (usually Cat3) cabling couldn’t handle 100 megabits. Some early implementations used four copper pairs (100BASE-T4) or fiber optics (100BASE-FX), but nearly every 100 megabit Ethernet connection today is  100BASE-TX, using plain two pairs on plain Cat5 cable.
  • Gigabit Ethernet had a similar history. Many were concerned that two pairs on unshielded Cat5 wiring could not handle 1000 megabits per second, so optical (1000BASE-SX) and balanced shielded wiring (1000BASE-CX) were specified. Although an unshielded 2-pair standard was developed (1000BASE-TX), it never really caught on. Therefore, today’s predominant gigabit LAN connection,  1000BASE-T, uses all four pairs of unshielded twister-pair wiring on a Cat5 cable (see note 1).
  • The 10 Gigabit Ethernet world has mostly shifted to the block coding scheme from Fibre Channel, 64B/66B, which is denoted by the letter “R”. This gives us a family of fiber optic cables (10GBASE-SR,  LR,  ER, etc), and a copper backplane interconnect (10GBASE-KR). The earlier copper wiring standard (10GBASE-CX4)  used InfiniBand-like 4-lane cables and 8B/10B signaling, as did  10GBASE-KX4  on the backplane. A backwards-compatible twisted-pair  10GBASE-T  has also been developed, but work continues to make it power-efficient enough to be practical (see note 2).
  • Looking ahead, we see  Higher-Speed Ethernet emerging:  40GBASE-KR4  for backplane use, multi-mode optical  40GBASE-SR4  and  100GBASE-SR10, and long-range single-mode optical  40GBASE-LR4  and  100GBASE-LR10.

As you can see, all this alphabet soup does have some consistency. Common unshielded twisted pair wiring is all “BASE-T”, optics are denoted according to their range (“S”, “L”, “E”), and backplanes use “K” copper. Clear as mud?

Note 1: Lots of people (and even equipment makers) incorrectly refer to common Gigabit Ethernet as “1000BASE-TX”, but this really should be called “1000BASE-T”.

Note 2: We will probably never see a  10GBASE-TX, which would use just 2 pairs of unshielded twisted pair copper wiring.

About the author

Stephen Foskett

Stephen Foskett is an active participant in the world of enterprise information technology, currently focusing on enterprise storage, server virtualization, networking, and cloud computing. He organizes the popular Tech Field Day event series for Gestalt IT and runs Foskett Services. A long-time voice in the storage industry, Stephen has authored numerous articles for industry publications, and is a popular presenter at industry events. He can be found online at,, and on Twitter at @SFoskett.

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